Air Conditioning for Hot-and and-humid Climates: Commercial Technologies ACEEE Market Transformation Conference Emerging Technologies March 21, 2007 Hugh I Henderson, Jr., P.E. CDH Energy Corp. Cazenovia, NY www.cdhenergy.com
Overview The Need for Humidity Control building applications with greatest need HVAC Control issues Technologies to Control Humidity active humidity control enhanced cooling systems ventilation pretreatment The Cost of Humidity Control which technologies are best?
What Should Humidity Levels Be? Maintain space below 60-65% RH
Where is Humidity a Concern? Applications with High Ventilation outdoor air is largest source of moisture Applications with Low Sensible Cooling Loads display cases in supermarkets provide cooling theatres with high occupancy, but no windows or lights Applications where HVAC Design/Controls Degrade Latent Performance evaporation of moisture from cooling coil when cooling is off but fan continues to operate
High Humidity Hours Houston Restaurant ASHRAE 1254-RP Final Report
High Humidity Hours Houston Office ASHRAE 1254-RP Final Report
Conventional Cooling Coil SHR = Sensible Sensible + Latent
Better Dehumidification means Lower Efficiency Kosar ASHRAE Journal 2006
Sensible and Latent Capacity With Continuous Supply Air Fan Operation Capacity (MBtu/h) 30 20 10 0 COIL1_TEST_4B_10B_16B_22B 08/30/02 07:42:04 Cycle #1 (Comp ON time: 45.0 minutes) Transition pt Latent Removal Sensible Off-Cycle Evaporation is Adiabatic Process: Sensible Latent -10 Compressor Latent Addition -20 0 20 40 60 80 100 time (minutes)
Latent Degradation at Part Load Shirey, Henderson & Raustad (2006) SHR 1.10 1.00 0.90 0.80 0.70 Continuous supply air fan operation Measured Data: averaged into 4 hour intervals entering RH: 57% to 63% entering air temp: 68F to 72F loop temps: 65F to 90F 0.0 0.2 0.4 0.6 0.8 1.0 Runtime Fraction (-) Latent Degradation Model with: t wet = 720 sec γ = 1.07 N max = 3.6 cyc/h τ = 75 sec linear decay Steady State SHR = 0.76
Novel Dehumidification Technologies Enthalpy wheels (recover heat and moisture) Gas-fired desiccant wheel systems Liquid desiccant systems Electric heat pump systems Thermally activated systems Hybrid electric desiccant system
Gas-fired Desiccant Wheel Unit Desiccant Technologies Liquid Desiccant Heat Pump (Drykor) Enthalpy Wheel
Recent Improvements Liquid Desiccants Low Flow Absorber low carryover 1-½ Effect Regeneration provides better efficiency More compatible with solar thermal (e.g., hot water) Thermally Activated Liquid Desiccant (AIL Research)
Recent Improvements Gas-Fired Hybrid Desiccants Hybrid Desiccant Unit (Semco) Smaller Desiccant Wheel treats a portion of supply air stream Desiccant likes cool high RH inlet air Hybrid approach uses advantages of each system
Recent Improvements Electric Hybrid Desiccants Munters HCU Combine desiccant wheel with vapor compression HCU uses condenser heat to regenerate desiccant wheel CDQ uses desiccant to enhances cooling coil SHR Cromer Cycle (Trane CDQ)
Improving AC Performance Lowering SHR Lower supply air flow rate (400 350 cfm/ton) Colder coil temperature (chilled water) Reheat supply air (using condenser heat) Subcool/reheat refrigeration circuit Ventilation Pretreatment
Enhanced AC Concepts Improving Conventional AC Sub/Cool Reheat (Carrier Humid-mizer) Condenser Reheat (Lennox Humiditrol)
Ventilation Pretreatment Dedicated Outside Air System (DOAS) or Makeup Air Units (MAU) Almost always makes sense! Outdoor Air MAU MAU Supply Air AC Unit Return Air AC Supply Air Building
Typical Theatre - Atlanta Simulation 250,000 Results Depends widely on application details Annual Energy Use (kwh) 200,000 150,000 100,000 50,000 - Base AC AC w/reheat MAU w/ Reheat HCU Vent Unit Fan Vent Unit AC Unit Fan AC Unit Fan power issues often drive annual results Hours per Year 4,500 4,000 3,500 3,000 2,500 2,000 1,500 Theatre - Atlanta Hrs > 60% RH OCCUPIED Hrs > 60% RH 1,000 500 - Base AC AC w/reheat MAU w/ Reheat HCU
ASHRAE Research 1254-RP Report Results available for various: Climates equipment types building applications ventilation assumptions
Summary Wide Spectrum of Dehumidification Technologies are Available Best solution depends on building application details Equipment configuration and controls also maters Hybrid Technologies look promising Ventilation pre-treatment is almost always a good idea in commercial applications